DESCRIPTION: Development of spatio-temporal receptive-field properties of retinal ganglion cells may be mediated by spontaneous embryonic electrical activity, neurite outgrowth and exposure to light at birth. The goal of this proposal is to investigate the following hypotheses. (1) The generation, duration and propagation of the embryonic retinal spontaneous bursts are mediated by excitatory synaptic connections, extracellular potassium or gap junctions; (2) dendritic outgrowth and establishment of excitatory synaptic connections onto immature dendrites are induced by spontaneous activity and terminated by exposure to light. These processes may account for the development of concentric fields and orientation selectivity; (3) the development of directional selectivity requires visual experience. The experiments designed to address these hypotheses will be performed in a turtle isolated-retina preparation, and they have three aims. I. To investigate the cellular mechanisms underlying the generation and the duration of embryonic spontaneous bursts, and to elucidate how neighboring embryonic ganglion cells fire in correlated bursts. Pharmacological manipulations and whole-cell patch clamp recordings will be used for that purpose. II. To test the proposed parallelism between the maturation of the dendritic layout and changes in receptive- field properties. Ganglion cells will be stained intracellularly with Neurobiotin (or horseradish peroxidase) after physiologically determining their receptive-field properties. III. To determine the role of 'environmental' factors, namely light and spontaneous activity on the development of these properties. Dark- induced changes will be investigated in hatchlings. The spontaneous correlated activity will be disrupted with intraocular implantations of the slow-release polymer Elvax 40W mixed with several drugs during development to determine how correlated spontaneous bursts mediate the development of receptive-field properties. This project will contribute to the understanding of how spontaneous embryonic correlated bursts and visual experience influence the development of retinal functions involved in processing visual information. Understanding these mechanisms in the retina will help us to achieve new insights into how highly complex integrative properties develop in the visual cortex.